Stable oil-extended synthetic rubbers

ABSTRACT

To improve the storage stability and degradation resistance of oil-extended solution-polymerized polymers of butadiene or isoprene, there is added 0.1 - 7 parts by weight based on the weight of rubber solids, of a proton acceptor, for example, benzidene, magnesium oxide, calcium stearate, sodium abietate, p, p&#39;&#39;-diamino-diphenyl methane, and the like.

United States Patent Nordsiek et al. 1 Sept. 2, 1975 [54] STABLE OIL-EXTENDED SYNTHETIC 3.019207 1 1962 Crane 260/336 RUBBERS 3081.276 3 1963 Snyder ct al. 260/336 3,180,858 4/1965 Farrar 260/94 3 1 Inventors: Karl-Heinz Nordsiek; J s 3,386,937 6/1968 Amberg.... 260 27 Schafer, both of Marl, Germany 3 397 167 8/1968 Gruver 260/33 6 3,457,218 7/1969 Haas ct al. 260/45 8 [731 Asslgnee: chem'sche we'ke 3,459,831 8/1969 Luftglass ct a1 260/336 x Aktiengesellschafl, MHFL Germany 3,497,489 2/1970 Saltman ct al. 260 947 x Filed: y 2' 1968 3,501,422 3/1970 Nordsick et al. 260/23.7 X

[211 Appl. No.: 726,239

P)I"IU' lzxummer-Eugene C. Rzucidlo Attorney, Agent, or FirnzMillen, Raptes & White [30] Foreign Application Priority Data May 8, 1967 Germany 42256 [57] ABSTRACT [52] US. Cl... 260/23.7 M; 260/27 BB; 260/237 R;

260/326 A; 260/336 AQ; 260/45.75 R; To improve the storage stability and degradation resis- 260/4585 R; 260/459 tzmce of oil-extended solution-polymerized polymers [51] Int. Cl. C08c 11/32 of butadiene 9r isoprene. there is added 7 p r Field f S h. 260/237 M, 33,6 AQ, 32,6 A by weight based on the weight of rubber solids, of a 260/4575, 94.7 A, 94.7 N, 45.9, 27 BU, 45.85 proton acceptor, for example, benzidene, magnesium oxide, calcium stearate, sodium abietate. pp- 56 References Ci d diamino-diphenyl methane, and the like.

UNITED STATES PATENTS 13 Claims, N0 Drawings 2.895.940 7/1959 Tucker 260/459 STABLE OIL-EXTENDED SYNTHETIC RUBBERS BACKGROUND OF THE INVENTION This invention relates to oil-extended rubbers, particularly to solution-polymerized polymers of isoprene or butadiene. I

Prior to vulcanization, oilextended synthetic rubbers normally suffer considerable molecular weight degradation during conventional processing and storage conditions. In this connection, insufficient storage stability has been a particular problem. Thus, several attempts have been made to solve this problem by employing a greater quantity of those additives conventionally used. as stabilizers for rubber, such as, for example, secondary ar'ylamines or stcrically hindered phenols. Unfortunately,it was soon discovered that these additives were not only unsuccessful, but they even increased the tendency of the rubber to degrade, this phenomenon being especially evident in the case of solution-polymerized polymers. 1

Bearing in mind that a marked decrease in the aver age molecular weight of the elastomer in the presence of extended oils, taking place during the course of storage and processing, is reflected in the corresponding fall off in the properties of the final vulcanizate, the im portance of the problem is readily apparent.

SUMMARY OE THE INVENTION solution has been discovered which is merely to add to the oil or the rubber-oil mixture an effective degradation-decreasing amount, preferably 0.1 7.0 parts by weight, based on 100 parts by weight of the solid rubber of a proton acceptor.

DETAILED DISCUSSION OF THE INVENTION Rubbers especially benefited by the invention because of their otherwise substantial degradation during storage or processing after being mixed with mineral oil plasticizers are particularly the high-cis-containing polybutadienes and polyisoprenes produced in solution, having a content of l,4-cis-configuration of, e.g., 30 100%, preferably above 40%. In addition, this invention is advantageous for the production of solutionpolymerized copolymers of butadiene and isoprene in all proportions, as well as copolymers of the aforesaid monomers with not more than about 40% by weight styrene. Aside from high-cis polymers and copolymers, this invention is also applicable to low-cis polymers and copolymers. for example. as produced on the basis of alkali metals, organometallic compounds, or redox systems in solution. Processes for producing both high-cis and low-cis polymers are well described in the literature, for example, G. Natta, Chimica e Industria 39 (l957), 733; R. F. Dunbrook et al., Proc. Rubber Technol. Conference, London 1954, page 139.

ture, including, butnot limited to, agents for terminat ing the polymerization (shortstops), and conventional 5 stabilizers.

The term proton acceptor is explained by the general definition of G. N. Lewis (all substances containing unshared electron pairs are bases). Especially suitable are oxides and hydroxides of the alkali and alkaline earth metals, as well as those of zinc and aluminum. The more common alkali and alkaline earth metals are: lithiurn, sodium, potassium, beryllium magnesium, calciurn, strontium,and barium. 1

The preferred dosage, in this connection, is '1 7.0 parts, particularly above 0.5 parts, and advantageously 2 parts by weight, based on 100 parts by weight of the proportion of solid rubber contained in the rubberoil mixture.

Aside from the inorganic proton acceptors, it also is beneficial to employ organic proton acceptors. Thus, rubber soluble primary amines of 2 20 carbon atoms are also suitable, for example, all saturated and unsaturated aliphatic and cycloaliphatic amines, monoand polynuclear arylamines, and alkanolaminesl In addition, there can be employed quaternary ammonium bases of tertiary aliphatic and cycloaliphatic amines of 4 15 carbon atoms, e.g., tetramethylammonium hydroxide or N-methylpiperidine-hydroxide.

It is preferred to employ primary arylamines such as aniline, p-phenylenediamine, benzidine, p,p-diaminodiphenyl-methane, naphthylamines, as well as the isomers and derivatives thereof. However, additionally suitable are certain aliphatic amines, such as, e.g., hexamethylenediamine, or heterocyclics, such as pyri- 'dine and piperidine. In connection with the solubility in the rubber phase, the-dosage, in this instance, is sufficient at 0.1 5 parts by weight, based on the solid rubber. General speaking suitable amines are those having a good solubility in the'rubbery material, being slightly volatilized by steam treatment, and also waterinsoluble.

It is furthermore possible to employ the alcoholates from alkali as well as alkaline earth metals and primary alcohols of l 12 carbon atoms.

Finally, alkaline-hydrolyzab le salts of organic acids can be employed with an especially advantageous effect, not only because of their stabilizing activity, but also because of other favorable effects on the rubber processing procedure. Predominantly suitable for this purpose are the alkali, alkaline earth, as well as zinc and aluminum salts of saturated and unsaturated carboxylic acids of 2 20 carbon atoms, particularly hydrocarbon carboxylic acids, especially higher fatty acids, such as stearic, palmitic, lauric, oleic and linoleic acid, as well as mixtures thereof.

Particularly preferred in this respectare the same salts of the rosin acids used in emulsion polymerization, and generally recognized as being advantageous, reference being directed to US. Pat. Nos. 2,450,416,

2,484,616, 2,569,448, 2,569,449 and 2,648,657 Hercules Powder Co.

The preferred dosages of the aforesaid salts range from 0.] 7 parts by weight, based on the proportion The conventional process steps of working up the product, as well as perhaps the further addition of conventional stabilizers. removal of solvents, separation of granules from the granule/water dispersion, as well as Of lid ru r. preliminary dewatering and drying of the granules, are

Important for obtaining the above-described stabilizconducted in the conventional manner. ing effect is the time of introducing the proton accep- In general, it is desirable for the polymers or copolytors during the production of the rubber-oil mixture. mers to have ML-4 values of about 30 to 150. Accord- Normally, the respective proton acceptor dissolved ingly, when proton acceptor shortstop agents are in an organic solvent inert with respect to the catalyst, added to the polymerization reactor, this should be or also in the form of a slurry is metered into the rubtaken into consideration. ber solution (before the rubber is precipitated) either Without further elaboration, it is believed that one before or after the extender oil is added. Another tech skilled in the art can, using the preceding description, nique is to mix the proton acceptor with the extender utilize the present invention to its fullest extent. The oil before it is added to the rubber. following preferred specific embodiments are, there- The stabilizing effect which is best by far is obtained fore, to be construed as merely illustrative, and not limwhen adding the proton acceptor as early as possible itative of the remainder of the specification and claims to the polymerization charge. In this connection, the in any way whatsoever. proton acceptor can serve simultaneously as the stabi- 7 EXA l 7 lizer and shortstop for the polymerization or molecular to weight (Mooney) jump reaction, so that the require- The examples are effectively set forth in the followment for a conventional shortstop is eliminated. In this ing table. connection, it is preferred for the proton acceptor to be After the polymerization process is terminated, the previously dissolved in the iner ol n p y additives set forth in the vertical column ll of the table ing the polymerization and then added in the form of re mixed into the solution of 1,4-cis-polybutadiene, such solution. By this technique, the purification of the t ether with 37 ,5 rts of extend r oil havi g a majo solvent, which is recycled and reused for the polymeriproportion by weight of aromatic compounds. The rubzation, is simplified, since the separation of an addiber obtained after working up and drying exhibits, is tional shortstop, e.g., methanol, is eliminated. Under tested by several stability tests, as listed in the table, these conditions, amounts of proton-acceptor as low as and compared to the control rubber not modified by 0.] 0.75 parts by weight of the rubber solids are comthe proton acceptor. pletely sufficient. Although, during the subsequent hy- The control sample, prepared in accordance with drolysis, the solution of the rubber-oil mixture has a conventional processes, containing a non-discoloring clearly acidic reaction, the stability previously induced g g Substance of the ri al y-hin r ph n l by the portion acceptor is not significantly diminished yp Specifically '-m hy n i -m hyl-6- rt.- if at all. Finally, though it is possible to admix the proy -p exhlblts, Under all Of the test Conditions, ton acceptor by means of rolls or an internal mixer to a decrease Mooney of about 35% 9 the the finished oil-rubber after working and drying, this Ha] Value- In Q P y the of the Proton procedure is less preferred since some degradation may cePtor according thls l the molecular even Occur during the admixing weight of the rubber is not significantly decreased.

TABLE I ll lll Proton IV V VI Vll Ex. Synthetic Addition of Acceptors Starting ML 4 ML 4 Mk4 Remarks No. Rubber (a) (b) (c) ML-4 After Roll After 8 hrs After 28 Type Amount Manner Treatment of Storage days of Parts by of Use l0 at at 120C Storage Weight 150C at C 1 cis-l,4- 40 l3 l6 l5 A polybutadiene 2 Benzidinc 4 dissolved 46 36 46 45 in benzene 3 Magnesium 7 slurried 40 34 39 38 oxide in benzene 4 Calcium 1.2 slurried 4O 38 37 Stearate in benzene 5 Sodium abi- 0.7 paste with 35 29 35 etate 30% water 6 p,p'di- 0.3 dissolved 47 47 47 43 B aminoin benzene diphenylmethane 7 Na-abie- 0.3 dissolved 32 2o 28 27 B tate in benzene s Na- 0.3 In form of 35 30 35 35 Nlethylate a slurrry in 9 -l-l- Dl-propylcnc 0.2 benzene triamine Dissolved in C benzene 40 35 39 40 Stabilized with a non-discoloring anti-aging substance. and containing 37.5 parts plasticizer oil per parts solid rubber.

4-i- Non-discoloring anti-aging substance not employed. A Comparative Example B The polymerization is stopped by adding llla.

C The polymerization is stopped by adding the amine.

The preceding examples can be repeated with similar success by substituting the generically and specifically described reactants and operating conditions of this invention for those used in the preceding examples.

From the foregoing description. one skilled in the art can easily ascertain the essential characteristics of this invention. and without departing from the spirit and scope thereof. can make various changes and modifications of the invention to adapt it to various usages and conditions. Consequently. such changes and modifications are properly. equitably, and intended to be, within the full range of equivalence of the following claims.

We claim: 1. In a process comprising l solution-polymerizing a monomer to form a rubber having 3()l()()/( cisconfiguration. said rubber being selected from the group consisting of polybutadiene and polyisoprene. admixing thereto l()7() parts oil per 100 parts solid rubber to form an oilextended rubber composition, and precipitating the oil-extended rubber from solutionjand 2. storing the composition; the improvement comprising dispersing in a solvent 0.1-7 parts by weight of a proton acceptor based on 100 parts by weight of said solid rubber. and

adding resultant dispersion to the rubber during polymerization and before said oil-extended rubber is precipitated from solution in step l said proton acceptor being a shortstop agent whereby the storage stability and degradation resistance of the rubber is substantially improved. and additional separate shortstop agent is not added to the polymerization milieu. said proton acceptor being A. a salt of an alkali metal, an alkaline earth metal, zinc or aluminum, the anion being of a carboxylic acid or 22() carbon atoms or a rosin acid;

B. an amine consisting essentially of a primary aromatic or aliphatic amine of 2-20 carbon atoms and not more than 3 nitrogen atoms and not more than 2 primary amino groups, said amine being soluble in rubber to the extent of at least 0. l().75 parts by weight of the rubber solids. being slightly volatilized by steam treatment and being water-insoluble;

C. a quaternary ammonium base of an aliphatic or cycloaliphatic tertiary amine of 4-15 carbon atoms.

2. A process as defined by claim I wherein said proton acceptor is a salt of an alkali metal, an alkaline earth metal, zinc or aluminum, the anion being of a carboxylic acid of 220 carbon atoms or a rosin acid.

3. A process as defined by claim 1 wherein said proton acceptor is a primary aromatic or aliphatic amine of 2-20 carbon atoms.

4. A process as defined by claim 1 wherein said proton acceptor is a quaternary ammonium base of an aliphatic or cycloaliphatic tertiary amine of 4l5 carbon atoms.

5. A process as defined by claim 1 wherein said rubber is polybutadiene.

6. A process as defined by claim 1 wherein saiid proton acceptor is selected from the group consisting of benzidine, calcium stearate, sodium abietate. and p.p'- diamino-diphenyl-methane.

7. A process as defined by claim 1 wherein said proton acceptor is an aliphatic amine of 2-2() carbon atoms.

8. A process as defined by claim 1 wherein said pro-.

ton acceptor is benzidine.

9. A proces as defined by claim 1 wherein said proton acceptor is calcium stearate.

10. A process as defined by claim 1 wherein said proton acceptor is sodium abietate.

l l. A process asdefined by claim 1 wherein said proton acceptor is p,p'-diamino-diphenyl-methane.

12. A process as defined by claim 1 wherein said aliphatic amine is hexamethylene diamine or dipropylene triamine.

13. A vulcanizable composition comprising an intimate mixture of a. an oil-extended. solution-polymerized rubber having 3()l()0% eis-configuration, said rubber being selected from the group consisting of polybutadiene and polyisoprene and containing 10-70 parts oil per parts solid rubber; and I b. 0.1 7 parts by weight of a proton acceptor based on 100 parts by weight solid rubber, said proton acceptor being benzidine, p,p'-diamino-diphenyl methane, or.

a quaternary ammonium base of an aliphatic or cycloaliphatic tertiary amine of 4-15 carbon atoms. 

1. IN A PROCESS COMPRISING
 1. SOLUTION-POLYMERIZING A MONOMER TO FORM A RUBBER HAVING 30-100% CIS-CONFIGURATION, SAID RUBBER BEING SELECTED FROM THE GROUP CONSISTING OF POLYBUTADIENE AND POLYISOPRENE, ADMIXING THERETO 10-70 PARTS OIL PER 100 PARTS SOLID RUBBER TO FORM AN OIL-EXTENDED RUBBER COMPOSITION, AND PRECIPITATING THE OIL-EXTENDED RUBBER FROM SOLUTION, AND
 2. storing the composition; the improvement comprising dispersing in a solvent 0.1-7 parts by weight of a proton acceptor based on 100 parts by weight of said solid rubber, and adding resultant dispersion to the rubber during polymerization and before said oil-extended rubber is precipitated from solution in step (1), said proton acceptor being a shortstop agent whereby the storage stability and degradation resistance of the rubber is substantially improved, and additional separate shortstop agent is not added to the polymerization milieu, said proton acceptor being A. a salt of an alkali metal, an alkaline earth metal, zinc or aluminum, the anion being of a carboxylic acid or 2-20 carbon atoms or a rosin acid; B. an amiNe consisting essentially of a primary aromatic or aliphatic amine of 2-20 carbon atoms and not more than 3 nitrogen atoms and not more than 2 primary amino groups, said amine being soluble in rubber to the extent of at least 0.1-0.75 parts by weight of the rubber solids, being slightly volatilized by steam treatment and being water-insoluble; or C. a quaternary ammonium base of an aliphatic or cycloaliphatic tertiary amine of 4-15 carbon atoms.
 2. A process as defined by claim 1 wherein said proton acceptor is a salt of an alkali metal, an alkaline earth metal, zinc or aluminum, the anion being of a carboxylic acid of 2-20 carbon atoms or a rosin acid.
 2. STORING THE COMPOSITION, THE IMPROVEMENT COMPRISING DISPERISING IN A SOLVENT 0.1-7 PARTS BY WEIGHT OF A PROTON ACCEPTOR BASED ON 100 PARTS BY WEIGHT OF SAID SOLID RUBBER, AND ADDING RESULTANT DISPERSION TO THE RUBBER DURING POLYMERIZATION AND BEFORE SAID OIL-EXTENDED RUBBER IS PRECIPITATED FROM SOLUTION IN STEP (1), SAID PROTON ACCEPTOR BEING A SHORTSTOP AGENT WHEREBY THE STORAGE STABILITY AND DEGRADATION RESISTANCE OF THE RUBBER IS SUBSTANTIALLY IMPROVED, AND ADDITIONAL SEPARATE SHORTSTOP AGENT IS NOT ADDED TO THE POLYMERIZATION MILIEU, SAID PROTON ACCEPTOR BEING A. A SALT OF AN ALKALI METAL, AN ALKALINE EARTH METAL, ZINC OR ALUMINUM, THE ANION BEING OF A CARBOXYLIC ACID OR 2-20 CARBON ATOMS OR A ROSIN ACID, B. AN AMINE CONSISTING ESSENTIALLY OF A PRIMARY AROMATIC OR ALIPHATIC AMINE OF 2-20 CARBON ATOMS AND NOT MORE THAN 3 NITROGEN ATOMS AND NOT MORE THAN 2 PRIMARY AMINO GROUPS, SAID AMINE BEING SOLUBLE IN RUBBER TO THE EXTENT OF AT LEAST 0.1-0.75 PARTS BY WEIGHT OF THE RUBBER SOLIDS, BEING SLIGHTLY VOLATILIZED BY STEAM TREATMENT AND BEING WATER-INSOLUBLE, OR C. A QUATERNARY AMMONIUM BASE OF AN ALIPHATIC OR CYCLOALIPHATIC TERTIARY AMINE OF 4-15 CARBON ATOMS.
 3. A process as defined by claim 1 wherein said proton acceptor is a primary aromatic or aliphatic amine of 2-20 carbon atoms.
 4. A process as defined by claim 1 wherein said proton acceptor is a quaternary ammonium base of an aliphatic or cycloaliphatic tertiary amine of 4-15 carbon atoms.
 5. A process as defined by claim 1 wherein said rubber is polybutadiene.
 6. A process as defined by claim 1 wherein saiid proton acceptor is selected from the group consisting of benzidine, calcium stearate, sodium abietate, and p,p''-diamino-diphenyl-methane.
 7. A process as defined by claim 1 wherein said proton acceptor is an aliphatic amine of 2-20 carbon atoms.
 8. A process as defined by claim 1 wherein said proton acceptor is benzidine.
 9. A proces as defined by claim 1 wherein said proton acceptor is calcium stearate.
 10. A process as defined by claim 1 wherein said proton acceptor is sodium abietate.
 11. A process as defined by claim 1 wherein said proton acceptor is p,p''-diamino-diphenyl-methane.
 12. A process as defined by claim 1 wherein said aliphatic amine is hexamethylene diamine or dipropylene triamine.
 13. A vulcanizable composition comprising an intimate mixture of a. an oil-extended, solution-polymerized rubber having 30-100% cis-configuration, said rubber being selected from the group consisting of polybutadiene and polyisoprene and containing 10-70 parts oil per 100 parts solid rubber; and b. 0.1 - 7 parts by weight of a proton acceptor based on 100 parts by weight solid rubber, said proton acceptor being benzidine, p,p''-diamino-diphenyl methane, or a quaternary ammonium base of an aliphatic or cycloaliphatic tertiary amine of 4-15 carbon atoms. 